1. Field of the Invention
The present invention generally relates to Power over Ethernet (PoE) devices, and more specifically to a power source equipment integrated circuit.
2. Related Art
Ethernet communications provide high speed data communications over a communications link between two communications nodes that operates according the IEEE 802.3 Ethernet Standard. The communications medium between the two nodes can be twisted pair wires for Ethernet, or other types communications medium that are appropriate. Power over Ethernet (PoE) communication systems provide power and data communications over a common communications link. More specifically, a power source device (PSE) connected to the physical layer of the first node of the communications link provides DC power (for example, 48 volts DC) to a powered device (PD) at the second node of the communications link. The DC power is transmitted simultaneously over the same communications medium with the high speed data from one node to the other node.
The PSE typically includes a controller that controls the DC power provided to the PD at the second node of the communications link. The PSE controller measures the voltage, current, and temperature of the outgoing and incoming DC supply lines to characterize the power requirements of the PD.
The PSE controller measures the current of using an embedded current measurement system. Conventional techniques for measuring the current requires measuring the voltage dissipated by a series resistor connected between a drain and a source of a large transistor. The size of the transistor must be large to safety handle the voltage and the current draw from the PD. As a result, a small value is chosen for the parallel resistor to conserve power. The small value of the parallel resistor reduces the ability to accurately measure the series resistor thereby diminishing the accuracy of the current measurement system.
Therefore, what is needed a current measurement system that is capable of accurately and efficiently measuring the current of a PD.